That is why it is plausible to
assume that the field becomes redundant in non-flying beetles. We examined the relationships between
the hind wing reduction and characters of this mechanosensory field in beetles of six families. We
measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory
field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous
species of the same body size. Further reduction of the sensory field in brachypterous species is obvious,
but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable
and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a
permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries
still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing
beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment
of such fringed wings in flying ptiliid species.